1. Field of the Invention
The present invention relates to a cover of an electronic component and a method for producing the same.
2. Description of the Related Art
An electronic component of interest for the present invention is a multi-layer substrate. In general, the multi-layer substrate includes a base, elements such as integrated circuits (ICs) or large scale integrated circuits (LSIs)) disposed on the base, and a cover formed of, for example, metal or resin. The base includes a lamination of a plurality of insulating layers having through holes and wiring circuits. The cover is arranged, for example, to protect the elements and to provide a flat adhesion surface required when mounting the cover to a mother board. However, when mounting the resin cover to the base whose surface to which the elements are mounted includes through holes, if the resin enters the openings of the through holes, conduction failure occurs.
To overcome this problem, Japanese Unexamined Patent Application Publication No. 2001-168493 discloses a method for producing an electronic component in which a metallic plate is provided for each through hole so as to cover each through hole, and thus, prevent the resin from entering each through hole.
According to the aforementioned document, however, in order to cover the through holes, it is necessary to dispose metallic plates that are larger than the area of the openings of the through holes. Therefore, in a small electronic component, elements cannot be mounted with such a small pitch.
An increase in wiring density tends to increase the number of through holes formed in the base, and a reduction in the size of the component tends to reduce the area of the openings of the through holes. Therefore, when each of the through holes is covered with a very small metallic plate as in the aforementioned document, costs are considerably increased. In addition, when the very small metallic plates are disposed at predetermined locations, gaps may be formed between the metallic plates and the openings of the through holes. If these gaps are formed, resin is not prevented from entering the through holes, and as a result, quality control problems are not entirely eliminated when mass production is considered.